package com.company.example.concurrent.lock;


import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * Created by ywl on 2017/2/15.
 * 共享锁
 */
public class TwinsLock implements Lock{
    private final Sync sync = new Sync(2);
    private static final class Sync extends AbstractQueuedSynchronizer {
        Sync(int count) {
            if(count <= 0) {
                throw new IllegalArgumentException("count must large than zero");
            }
            setState(count);
        }

        public int tryAcquireShared(int reduceCount){
            for(;;){
                int current = getState();
                int newCount = current - reduceCount;
                if(newCount < 0 || compareAndSetState(current,newCount)) {
                    return newCount;
                }
            }
        }

        public boolean tryReleaseShared(int reduceCount){
            for (;;){
                int current = getState();
                int newCount = current + reduceCount;
                if(compareAndSetState(current,newCount)) {
                    return true;
                }
            }
        }
    }

    @Override
    public void lock() {
        sync.acquireShared(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    @Override
    public boolean tryLock() {
        return false;
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireSharedNanos(1,unit.toNanos(time));
    }

    @Override
    public void unlock() {
        sync.releaseShared(1);
    }

    @Override
    public Condition newCondition() {
        return null;
    }
}
